Chain conveyors are used in various applications, such as in vehicle assembly. In a conventional chain conveyor, sprockets are arranged on the left and right sides of the conveyor path, both at the front end and at the rear end of the conveyor. A first chain is engaged with the sprockets on the left side, and a second chain is engaged with the sprockets on the right side. The chains reverse their direction of travel as they pass over the sprockets at the front and rear ends of the conveyor. Slat plates, connected to the chain links, extend, transverse to the path of conveyor travel, from one chain to the other.
A typical vehicle assembly conveyor is shown and described in Japanese Laid-Open Patent Publication No. 2003-165605. In that conveyor, vehicle-supporting trays are sequentially placed on a slat conveyor, and a raised working floor, on which assembly workers ride, is formed on the conveyor, between the successive trays, by treads attached to the slat plates.
In chain conveyors such as the slat conveyor disclosed in Japanese Laid-Open Patent Publication No. 2003-165605, it is conventional for the chain pitch to be large compared to the chain pitch of a transmission chain.
United States Patent application publication No. US2004/0002402 shows and describes a typical conveyor chain. The tooth forms of a sprockets which engage with the endless conveyor chain are symmetrical, and the tooth thickness becomes progressively smaller toward the tooth head, so that the chains and the sprockets can engage smoothly without interference.
However, because of the larger chain pitch, large pulsations and speed variations of the chain are generated due to polygonal motion. These pulsations and speed variations are a problem in chain conveyors, especially in assembly lines for automobiles, electrical appliances and the like, where workers ride on the conveyor, and also in the case of escalators. In the case of an assembly line conveyor, pulsations and speed variations make assembly work difficult. Moreover, in the case of an assembly line conveyor, and in an escalator as well, the pulsations and speed variations result in an uncomfortable ride.
In the case of an escalator, a smaller chain pitch has been used in order to improve rider comfort, but the smaller chain pitch results in significantly increased costs because of the high parts count.
A general object of this invention is to solve the aforementioned problems of pulsations and speed variations.
More particularly, it is an object of the invention to provide a conveyance system in which vertical movement of the endless roller chains or bushing chains, due to polygonal motion, is reduced. It is also an object of the invention to enable the rollers of the chain (or bushings in the case of a bushing-type chain) to disengage smoothly from the sprockets. Finally, it is an object of the invention to suppress pulsations and speed variations resulting from polygonal motion, and to achieve stable conveyance of articles so that working conditions and comfort on the conveyor are improved.